Sanford Meeks - Academia.edu (original) (raw)

Papers by Sanford Meeks

Medical Physics, Jun 1, 2006

Purpose: To develop an on‐line patient alignment procedure that fully utilizes the CT guidance an... more Purpose: To develop an on‐line patient alignment procedure that fully utilizes the CT guidance and dose verification feasibility in image guided radiotherapy. The new patient position is selected to optimize the plan that is evaluated using the daily contours created based on deformable image registration.Method and Materials: Before a treatment fraction is delivered, a CTimage of the patient in the treatment position is obtained. The couch is adjusted to match the planning CTimage via on‐line image guidance. Verification dose is calculated using this daily image. A deformable registration between the planning image and the daily image is performed and the ROIs are automatically re‐contoured on the daily image. The daily dose is mapped back to the planning frame and then accumulated with the previous fraction dose. The new patient position is chosen via a procedure that optimizes the plan evaluated using the daily ROIs. The whole procedure entails the sequential execution of the following tasks: daily CT, CT‐guided patient setup, deformable registration and automatic re‐contouring, deformation of dose back to reference CT,dose‐based patient position optimization, and plan evaluation using cumulative and daily doses.Results: The new couch alignment procedure was validated on clinical prostate cancer data that includes a planning CTimage and 17 fraction CTimages (256×256×47) with resolution of 0.1875×0.1875×0.3cm3. The whole procedure was completed in a few minutes. The DVH results indicated improved sparing of the sensitive structures and better target coverage. Conclusion: The new dose‐based patient alignment procedure is an advancement to the image guidance alignment alone. Notable improvement in delivery dose can be achieved for certain types of treatment sites such as prostate cancer where the inter‐faction positions of target relative to sensitive structures are not well correlated with the positions of rigid structures and are difficult to predict.

Biomedical Physics & Engineering Express

Though potentially beneficial, proton beam stereotactic radiosurgery has not been adopted widely ... more Though potentially beneficial, proton beam stereotactic radiosurgery has not been adopted widely secondary to the technical challenge of safely delivering multiple focused beams of proton radiation. In this study, we describe the design and characterization of a proton beam stereotactic radiosurgery system that can be adopted by existing passive scattering systems. This system utilizes a helmet-like device in which patient-specific brass apertures required for final beam collimation are positioned on a scaffold that is separate from the treatment gantry. The proton snout is then fitted with a generic aperture to focus the primary proton beam onto the patient specific apertures that are in the helmet-like device. The patient-specific apertures can all be placed at the start of the treatment, thus treatment with multiple beams can be accomplished without the delay of switching the apertures. In this report we describe a prototype design of this collimation system and dosimetric testing to verify efficacy. Subsequently, we describe a custom 3D printing of a prototype device and report on overall localization accuracy using Winston-Lutz tests. Our results show that it is possible to develop an add-on device for proton beam radiosurgery that is safe and efficient and capable of wide adoption on existing proton delivery systems.

Practical Radiation Oncology

International Journal of Particle Therapy

Purpose We present an analysis of various operational metrics for a novel compact proton therapy ... more Purpose We present an analysis of various operational metrics for a novel compact proton therapy system, including clinical case mix, subsystems utilization, and quality assurance trends in beam delivery parameters over a period of 5 years. Materials and Methods Patient-specific data from a total of 850 patients (25,567 fractions) have been collected and analyzed. The patient mix include a variety of simple, intermediate, and complex cases. Beam-specific delivery parameters for a total of 3585 beams were analyzed. In-room imaging system usage for off-line adaptive purpose is reported. We also report key machine performances metrics based on routine quality assurance in addition to uptime. Results Our analysis shows that system subcomponents including gantry and patient positioning system have maintained a tight mechanical tolerance over the 5-year period. Various beam parameters were all within acceptable tolerances with no clear trends. Utilization frequency histograms of gantry an...

Journal of Applied Clinical Medical Physics

Purpose: The purpose of this study was to evaluate the performance of three common deformable ima... more Purpose: The purpose of this study was to evaluate the performance of three common deformable image registration (DIR) packages across algorithms and institutions. Methods and Materials: The Deformable Image Registration Evaluation Project (DIREP) provides ten virtual phantoms derived from computed tomography (CT) datasets of head-and-neck cancer patients over a single treatment course. Using the DIREP phantoms, DIR results from 35 institutions were submitted using either Velocity, MIM, or Eclipse. Submitted deformation vector fields (DVFs) were compared to ground-truth DVFs to calculate target registration error (TRE) for six regions of interest (ROIs). Statistical analysis was performed to determine the variability between each DIR software package and the variability of users within each algorithm. Results: Overall mean TRE was 2.04 ± 0.35 mm for Velocity, 1.10 ± 0.29 mm for MIM, and 2.35 ± 0.15 mm for Eclipse. The MIM mean TRE was significantly different than both Velocity and Eclipse for all ROIs. Velocity and Eclipse mean TREs were not significantly different except for when evaluating the registration of the cord or mandible. Significant differences between institutions were found for the MIM and Velocity platforms. However, these differences could be explained by variations in Velocity DIR parameters and MIM software versions. Conclusions: Average TRE was shown to be <3 mm for all three software platforms. However, maximum errors could be larger than 2 cm indicating that care should be exercised when using DIR. While MIM performed statistically better than the other packages, all evaluated algorithms had an average TRE better than the largest voxel dimension. For the phantoms studied here, significant differences between algorithm users were minimal suggesting that the algorithm used may have more impact on DIR accuracy than the particular registration technique employed. A significant difference in TRE was discovered between MIM versions showing that DIR QA should be performed after software upgrades as recommended by TG-132.

Journal of Clinical Medicine, 2022

With the implementation of MR-LINACs, real-time adaptive radiotherapy has become a possibility wi... more With the implementation of MR-LINACs, real-time adaptive radiotherapy has become a possibility within the clinic. However, the process of adapting a patient’s plan is time consuming and often requires input from the entire clinical team, which translates to decreased throughput and limited patient access. In this study, the authors propose and simulate a workflow to address these inefficiencies in staffing and patient throughput. Two physicians, three radiation therapists (RTT), and a research fellow each adapted bladder and bowel contours for 20 fractions from 10 representative patient plans. Contouring ability was compared via calculation of a Dice Similarity Index (DSI). The DSI for bladder and bowel based on each potential physician–therapist pair, as well as an inter-physician comparison, exhibited good overlap amongst all comparisons (p = 0.868). Plan quality was compared through calculation of the conformity index (CI), as well as an evaluation of the plan’s dose to a ‘gold s...

International Journal of Particle Therapy, 2021

Purpose To present quantitative dosimetric evaluations of five proton pencil beam spot placement ... more Purpose To present quantitative dosimetric evaluations of five proton pencil beam spot placement techniques. Materials and Methods The spot placement techniques that were investigated include two grid-based (rectilinear grid and hexagonal grid, both commonly available in commercial planning systems) and three boundary-contoured (concentric contours, hybrid, and optimized) techniques. Treatment plans were created for two different target volumes, one spherical and one conical. An optimal set of planning parameters was defined for all treatment plans and the impact of spot placement techniques on the plan quality was evaluated in terms of lateral/distal dose falloff, normal tissue sparing, conformity and homogeneity of dose distributions, as well as total number of spots used. Results The results of this work highlight that for grid-based spot placement techniques, the dose conformity is dependent on target cross-sectional shape perpendicular to beam direction, which changes for each ...

Physics in Medicine & Biology, 2019

Maintaining a sharp lateral dose falloff in pencil beam scanning (PBS) proton therapy is crucial ... more Maintaining a sharp lateral dose falloff in pencil beam scanning (PBS) proton therapy is crucial for sparing organs at risk (OARs), especially when they are in close proximity to the target volume. The most common approach to improve lateral dose falloff is through the use of physical beam shaping devices, such as brass apertures or collimator based systems. A recently proposed approach focuses on proton beam spot placements, moving away from traditional grid-based placements to concentric-contours based schemes. This improves lateral dose falloff in two ways: 1) by better conforming all spots to the tumor boundary and 2) allowing for "edge enhancement", where boundary spots deliver higher fluence than more central spots, thereby creating a steeper lateral dose falloff. However, these benefits come at the expense of maintaining uniformity of spot distribution inside the target volume. In this work we have developed a new optimized spot placement scheme that provides robust spot distributions inside the target. This approach achieves the boundary conformity of a concentric-contours based approach and uses a fast-iterative method to distribute the interior spots in a highly uniform fashion in an attempt to improve both the lateral dose falloff and uniformity. Furthermore, we quantified the impact of this new approach through direct comparison with grid, contour, and hybrid spot placements schemes, showing improvements for this new approach. The results were validated in homogeneous medium for two different target shapes having concave and convex geometry.

International Journal of Radiation Oncology*Biology*Physics, 2017

Purpose/Objective(s): Heterotopic ossification is a debilitating form of dystrophic calcification... more Purpose/Objective(s): Heterotopic ossification is a debilitating form of dystrophic calcification that occurs in 50-90% of patients with traumatic acetabular fractures. Radiation therapy in the peri-operative period is a proven intervention to reduce the incidence of heterotopic ossification. However, as many of the patients requiring radiation have suffered polytrauma and/or are clinically unstable, the treatment of these patients can be logistically challenging, uncomfortable for the patient and, at times, clinically unsafe. In this study, we describe the development and characterization of a clinical protocol in which the diagnostic images obtained on patients requiring radiation therapy for HO prophylaxis can be used for radiation treatment planning. This protocol allows for individualized patient treatment plans to be generated and transferred to the record and verify system prior to the patient being brought to the department for therapy. Using this method, these often times critically ill patients can be treated with improved efficiency and safety. Materials/Methods: We retrospectively identified 10 patients treated in 2015 in our department after traumatic hip fracture for heterotopic ossification prophylaxis who had undergone CT simulation for treatment planning. The diagnostic CT scans of the patients obtained by orthopedic surgery immediately post operatively to examine hardware placement were imported into the MIMvista system and corrected for orientation and then adjusted to a neutral pelvis alignment. These scans were then imported into the Pinnacle treatment planning system and plans were designed to treat the affected hip to 7.5 Gy in 1 fraction per institutional standard for HO prophylaxis. In order to determine the safety of this protocol, the treatment plans were then transferred without alteration onto the CT data set obtained at the time of CT simulation, and the dose distributions were compared. Results: There were limited differences in the dose distributions in the plans generated on the diagnostic scans and dose distributions after transfer to the CT simulation data sets. The maximum point dose was within 1% (range-1% to 1%), and the volumes receiving 7.5 Gy and 7.0 Gy were within 25% (range,-25% to 20%) and 6% (range-3% to 6%) respectively. Additionally, the treatment plans after transfer to the CT simulation data sets were each reviewed by four physicians in the department not involved in the replanning portion of the study, and 100% of the plans were felt to be appropriate for treatment. Conclusion: This study demonstrates that diagnostic imaging scans can reasonably be used to plan patients requiring radiation for heterotopic ossification prophylaxis. As a result, patients can be treated efficiently, potentially reducing the time they will spend in the department and improving patient safety.

Medical Physics, 2006

Helical tomotherapy using the Hi‐ART II is analogous to helical CTimaging where the gantry and th... more Helical tomotherapy using the Hi‐ART II is analogous to helical CTimaging where the gantry and the couch are in simultaneous motion. Hence, beam delivery is continuous over all 360 in transverse planes about the patient. Temporal beam modulation is achieved by using a binary multi‐leaf collimator. In addition to its ability to deliver IMRT, the Hi‐ART II has the ability to obtain helical megavoltage CT (MVCT) images. These MVCT images have adequate spatial and contrast resolution for image guidance, and also for identification of many soft‐tissue structures. The incorporation of daily three dimensional soft‐tissue imaging into the radiotherapy process also enables dose recalculation and periodic evaluation of the treatment delivery during a course of radiotherapy. Hence, the subsequent treatment delivery can be modified using a systematic feedback of the geometric and dosimetric information in the previous fractions. This requires many components as feedback, including CT guidance to achieve soft tissue localization, dose recalculation, dose accumulation, treatment evaluation, re‐contouring, and re‐optimization. This lecture will provide an overview of the physical characteristics of the Hi‐ART II, acceptance testing and commissioning, image quality tests, image registration, basic quality assurance, and an overview of clinical applications. Finally, system limitations and future developments will be addressed. Educational Objectives 1. Understand the basics concepts of helical tomotherapy. 2. Understand the basic QA requirements and system limitations association with helical tomotherapy. 3. Understand the workflow and issues related to clinical applications of helical tomotherapy, including acquisition, reconstruction, registration and patient alignment. 4. Understand the possibilities of daily soft‐tissue imaging for patient alignment and evaluation of treatment accuracy.

Medical Physics, 2006

Purpose: To develop a fast scan‐plan‐treat mode that can deliver breast treatments within 15 minu... more Purpose: To develop a fast scan‐plan‐treat mode that can deliver breast treatments within 15 minutes Method and Materials: With the advent of on‐line CTimaging capability, it becomes increasingly feasible to use a radiation therapy system as a single‐source device to image, plan, and deliver a patient treatment, in as little as 10–20 minutes from patient entry to exit. Such a mode can be particularly useful for cord compressions and emergency treatments. This concept is here expanded to deliver breast treatments using topotherapy, or a radiation therapytreatmentdelivered with concurrent couch motion but with a fixed gantry angle. MLC modulation may accompany this motion. The goal of this work was to explore: Whether auto‐contouring could be used to define breast and sensitive structures. Whether this process could be completed in 10‐20 minutes. The adequacy of the plans given the time constraints on both optimization and deliveryResults: It was determined that auto‐contouring could successfully contour the ipsilateral breast, the contralateral breast, each lung, and the trachea in less than 1 minute. Planning could be completed in less than 5 minutes through use of an optimization template, along with less than 5 minutes for imaging, and less than 5 minutes for delivery of 2 topographic angles. The plan optimized in this manner treated the target breast with a homogeneity of +/− 5%, and sensitive structure sparing equivalent to a conventional breast plan. Subsequent fractions can be currently created with this tool, or treated with alternate off‐line optimizations. Conclusion: The scan‐plan‐treat paradigm can be combined with a topotherapy‐style delivery to enable breast treatments in less than 20 minutes from the time a patient first enters the clinic. This work was supported by TomoTherapy Inc.

Medical Physics, 2006

ABSTRACT

Medical Physics, 2010

Optical guidance (OG) such as optical distance indicator (ODI) in‐room laser alignment and live‐v... more Optical guidance (OG) such as optical distance indicator (ODI) in‐room laser alignment and live‐video camera monitoring has been routinely used in conventional radiotherapy for patient setup and monitoring. Now emerging OG using optical tracking and topologic imaging (stereovision) techniques can provide remote operators with real‐time measurements of patient body (or support apparatus) position shape and movement. The temporal and spatial OG will be an essential component in any advanced image‐guidedradiotherapy(IGRT) when patient or organ motion are considered during the dose delivery. In assisting users to become familiar with the new OG techniques this education session will start with an introduction on basic photogrammetry general camera calibration triangulation principle for 3D optical imagingsurface extraction and registration and what OG systems can and cannot do. Then the session will move to the clinical use of infrared patient positioning and tracking systems (IPT) with particular attention to the combined use with other imagingsystems detection and correction with six degrees of freedom for rigid body displacement and issues in attachment of the infrared reflection markers. That will lead up to actual use ISG integrated stereovision‐guided patient reposition and monitoring systems focusing on quantification of the body position and displacement prior to and during beam or arc irradiation. ISG adaptive radiotherapy of the brain H&N lung and breast cancer will be demonstrated using examples from early clinical trials. The effects of target motion and deformation skin tones and room light conditions are also discussed. Learning Objectives: 1. Understand the spatial and temporal characteristics of advanced OG 2. Understand the basic operation principle of 3D optical systems 3. Know how to check and calibrate the optical camerasystems 4. Understand why multiple infrared reflection markers have to be fastened to the patient 5. Know how to quantify and correct the displacements with six‐degrees of freedom 6. Know how to surrogate optical surfaceimages with CT/MR volumetric images 7. Know how to acquire reliable surfaceimages prior to and during X‐ray irradiation 8. Understand the limits and benefits in application of OG in clinical settings

Medical Dosimetry, 1996

It is well established that the beam fluence on the central axis for rectangular or blocked field... more It is well established that the beam fluence on the central axis for rectangular or blocked fields is not always the same as that of its collimator equivalent square field. Many centers still determine monitor unit settings using a single output factor based on the collimator equivalent square field size because they feel the small errors introduced by this approach do not justify the extra data and effort required to correctly determine the monitor unit settings. Analyzing clinical monitor unit determinations for 6 and 15 MV photon irradiation. it is shown that failure to account for these discrepancies in central axis beam fluence may introduce 2.5-3% error in clinical situations. While the error is generally small, it must be eliminated if we intend to reach the commonly stated goal of 5% overall uncertainty in dose determination.

International Journal of Radiation Oncology*Biology*Physics, 2007

International Journal of Radiation Oncology*Biology*Physics, 2005

Purpose/Objective: Multiple definitions have been proposed to define successful biochemical outco... more Purpose/Objective: Multiple definitions have been proposed to define successful biochemical outcome (bNED) following definitive irradiation for prostate cancer. When the ASTRO consensus definition (ACD) and the Houston/current PSA nadir ϩ 2 (CNϩ2) definitions have been applied to the same patients treated with external beam irradiation (EBRT), substantial variation in bNED rates has been noted. The CNϩ2 definition has been reported to offer better sensitivity and specificity with regard to ultimate clinical failure. Whether or not these definitions provide similar or conflicting results when applied to prostate brachytherapy patients is uncertain. This study compares the bNED outcome using these two different definitions for patients undergoing permanent, pre-planned, transperineal ultrasound-guided interstitial I-125 prostate brachytherapy (PB), and their relationship with clinical failure (CF). Materials/Methods: 304 consecutive PB patients implanted between 1/1/98 and 3/31/01 were retrospectively evaluated. Median PSA follow-up was 52 months (maximum 80 months; 100 patients had follow-up in excess of 5 years). Patients had either low-or intermediate-risk disease. No patient received EBRT or post-PB adjuvant androgen deprivation. The prescribed dose was 144-145 Gy (TG43). The median implant activity was 40 mCi (range 24-57); the median prostate planning ultrasound volume was 38 ml (range 16-61). Median day-30 post-PB CT dosimetry values were V-100ϭ95%, V-150ϭ61%, and D-90ϭ162 Gy; median post-PB CT prostate volume was 46 ml (range 20-90). The primary endpoint for this analysis was the bNED rate determined by the ACD and CNϩ2 definitions. CF was defined as when documented local, regional, or distant recurrence developed, or when salvage hormonal therapy was initiated for biochemical failure alone. Freedom from salvage therapy (FSRx), disease-specific survival (DSS), and overall survival (OS) were also assessed. The Kaplan-Meier method was used to calculate 5-year actuarial results. Results: The 5-year bNED rate using ACD was 95%; the corresponding rate using CNϩ2 was 94%. 4 patients developed CF and all received immediate salvage androgen deprivation (SAD): 1 for distant metastasis, 1 for regional nodal failure, 1 for simultaneous local recurrence with distant metastasis; a 4th patient received SAD for biochemical failure alone. No patient experienced isolated local recurrence. There were no prostate cancer or treatment-related deaths. The 5-year FSRx rate was 98%; the 5-year DSS rate was 100%, and the 5-year OS rate was 97%. 94 (31%) of patients experienced PSA "bounce." ACD identified 15 failures; CNϩ2 identified 10 failures. This difference is due to 5 ACD failure patients with PSA nadirs between 0.2-0.5, who have, at last follow-up, slowly rising PSA values below the CNϩ2 PSA failure threshold (most recent PSA range 0.9-1.8). 3 of these 5 have undergone repeat prostate biopsies 60ϩ months post-PB; all re-biopsies were negative, and none of the 5 has regional or distant recurrence on restaging prostascint and bone scans. For detecting CF, both definitions demonstrated equal sensitivity (1.00); however, the CNϩ2 definition demonstrated higher specificity (0.98 vs 0.96), a higher positive predictive value (0.40 vs 0.27), and a higher positive likelihood ratio (50 vs 27). Conclusions: In contrast to results reported from EBRT treated patients, the ACD and CNϩ2 definitions of biochemical failure provided near-equivalent 5-year bNED rates for patients treated with PB. However, CNϩ2 more accurately identified PB patients who experienced CF and required salvage treatment.

… in Medicine and …, 2008

Medical Physics, Jun 1, 2006

Purpose: To develop an on‐line patient alignment procedure that fully utilizes the CT guidance an... more Purpose: To develop an on‐line patient alignment procedure that fully utilizes the CT guidance and dose verification feasibility in image guided radiotherapy. The new patient position is selected to optimize the plan that is evaluated using the daily contours created based on deformable image registration.Method and Materials: Before a treatment fraction is delivered, a CTimage of the patient in the treatment position is obtained. The couch is adjusted to match the planning CTimage via on‐line image guidance. Verification dose is calculated using this daily image. A deformable registration between the planning image and the daily image is performed and the ROIs are automatically re‐contoured on the daily image. The daily dose is mapped back to the planning frame and then accumulated with the previous fraction dose. The new patient position is chosen via a procedure that optimizes the plan evaluated using the daily ROIs. The whole procedure entails the sequential execution of the following tasks: daily CT, CT‐guided patient setup, deformable registration and automatic re‐contouring, deformation of dose back to reference CT,dose‐based patient position optimization, and plan evaluation using cumulative and daily doses.Results: The new couch alignment procedure was validated on clinical prostate cancer data that includes a planning CTimage and 17 fraction CTimages (256×256×47) with resolution of 0.1875×0.1875×0.3cm3. The whole procedure was completed in a few minutes. The DVH results indicated improved sparing of the sensitive structures and better target coverage. Conclusion: The new dose‐based patient alignment procedure is an advancement to the image guidance alignment alone. Notable improvement in delivery dose can be achieved for certain types of treatment sites such as prostate cancer where the inter‐faction positions of target relative to sensitive structures are not well correlated with the positions of rigid structures and are difficult to predict.

Biomedical Physics & Engineering Express

Though potentially beneficial, proton beam stereotactic radiosurgery has not been adopted widely ... more Though potentially beneficial, proton beam stereotactic radiosurgery has not been adopted widely secondary to the technical challenge of safely delivering multiple focused beams of proton radiation. In this study, we describe the design and characterization of a proton beam stereotactic radiosurgery system that can be adopted by existing passive scattering systems. This system utilizes a helmet-like device in which patient-specific brass apertures required for final beam collimation are positioned on a scaffold that is separate from the treatment gantry. The proton snout is then fitted with a generic aperture to focus the primary proton beam onto the patient specific apertures that are in the helmet-like device. The patient-specific apertures can all be placed at the start of the treatment, thus treatment with multiple beams can be accomplished without the delay of switching the apertures. In this report we describe a prototype design of this collimation system and dosimetric testing to verify efficacy. Subsequently, we describe a custom 3D printing of a prototype device and report on overall localization accuracy using Winston-Lutz tests. Our results show that it is possible to develop an add-on device for proton beam radiosurgery that is safe and efficient and capable of wide adoption on existing proton delivery systems.

Practical Radiation Oncology

International Journal of Particle Therapy

Purpose We present an analysis of various operational metrics for a novel compact proton therapy ... more Purpose We present an analysis of various operational metrics for a novel compact proton therapy system, including clinical case mix, subsystems utilization, and quality assurance trends in beam delivery parameters over a period of 5 years. Materials and Methods Patient-specific data from a total of 850 patients (25,567 fractions) have been collected and analyzed. The patient mix include a variety of simple, intermediate, and complex cases. Beam-specific delivery parameters for a total of 3585 beams were analyzed. In-room imaging system usage for off-line adaptive purpose is reported. We also report key machine performances metrics based on routine quality assurance in addition to uptime. Results Our analysis shows that system subcomponents including gantry and patient positioning system have maintained a tight mechanical tolerance over the 5-year period. Various beam parameters were all within acceptable tolerances with no clear trends. Utilization frequency histograms of gantry an...

Journal of Applied Clinical Medical Physics

Purpose: The purpose of this study was to evaluate the performance of three common deformable ima... more Purpose: The purpose of this study was to evaluate the performance of three common deformable image registration (DIR) packages across algorithms and institutions. Methods and Materials: The Deformable Image Registration Evaluation Project (DIREP) provides ten virtual phantoms derived from computed tomography (CT) datasets of head-and-neck cancer patients over a single treatment course. Using the DIREP phantoms, DIR results from 35 institutions were submitted using either Velocity, MIM, or Eclipse. Submitted deformation vector fields (DVFs) were compared to ground-truth DVFs to calculate target registration error (TRE) for six regions of interest (ROIs). Statistical analysis was performed to determine the variability between each DIR software package and the variability of users within each algorithm. Results: Overall mean TRE was 2.04 ± 0.35 mm for Velocity, 1.10 ± 0.29 mm for MIM, and 2.35 ± 0.15 mm for Eclipse. The MIM mean TRE was significantly different than both Velocity and Eclipse for all ROIs. Velocity and Eclipse mean TREs were not significantly different except for when evaluating the registration of the cord or mandible. Significant differences between institutions were found for the MIM and Velocity platforms. However, these differences could be explained by variations in Velocity DIR parameters and MIM software versions. Conclusions: Average TRE was shown to be <3 mm for all three software platforms. However, maximum errors could be larger than 2 cm indicating that care should be exercised when using DIR. While MIM performed statistically better than the other packages, all evaluated algorithms had an average TRE better than the largest voxel dimension. For the phantoms studied here, significant differences between algorithm users were minimal suggesting that the algorithm used may have more impact on DIR accuracy than the particular registration technique employed. A significant difference in TRE was discovered between MIM versions showing that DIR QA should be performed after software upgrades as recommended by TG-132.

Journal of Clinical Medicine, 2022

With the implementation of MR-LINACs, real-time adaptive radiotherapy has become a possibility wi... more With the implementation of MR-LINACs, real-time adaptive radiotherapy has become a possibility within the clinic. However, the process of adapting a patient’s plan is time consuming and often requires input from the entire clinical team, which translates to decreased throughput and limited patient access. In this study, the authors propose and simulate a workflow to address these inefficiencies in staffing and patient throughput. Two physicians, three radiation therapists (RTT), and a research fellow each adapted bladder and bowel contours for 20 fractions from 10 representative patient plans. Contouring ability was compared via calculation of a Dice Similarity Index (DSI). The DSI for bladder and bowel based on each potential physician–therapist pair, as well as an inter-physician comparison, exhibited good overlap amongst all comparisons (p = 0.868). Plan quality was compared through calculation of the conformity index (CI), as well as an evaluation of the plan’s dose to a ‘gold s...

International Journal of Particle Therapy, 2021

Purpose To present quantitative dosimetric evaluations of five proton pencil beam spot placement ... more Purpose To present quantitative dosimetric evaluations of five proton pencil beam spot placement techniques. Materials and Methods The spot placement techniques that were investigated include two grid-based (rectilinear grid and hexagonal grid, both commonly available in commercial planning systems) and three boundary-contoured (concentric contours, hybrid, and optimized) techniques. Treatment plans were created for two different target volumes, one spherical and one conical. An optimal set of planning parameters was defined for all treatment plans and the impact of spot placement techniques on the plan quality was evaluated in terms of lateral/distal dose falloff, normal tissue sparing, conformity and homogeneity of dose distributions, as well as total number of spots used. Results The results of this work highlight that for grid-based spot placement techniques, the dose conformity is dependent on target cross-sectional shape perpendicular to beam direction, which changes for each ...

Physics in Medicine & Biology, 2019

Maintaining a sharp lateral dose falloff in pencil beam scanning (PBS) proton therapy is crucial ... more Maintaining a sharp lateral dose falloff in pencil beam scanning (PBS) proton therapy is crucial for sparing organs at risk (OARs), especially when they are in close proximity to the target volume. The most common approach to improve lateral dose falloff is through the use of physical beam shaping devices, such as brass apertures or collimator based systems. A recently proposed approach focuses on proton beam spot placements, moving away from traditional grid-based placements to concentric-contours based schemes. This improves lateral dose falloff in two ways: 1) by better conforming all spots to the tumor boundary and 2) allowing for "edge enhancement", where boundary spots deliver higher fluence than more central spots, thereby creating a steeper lateral dose falloff. However, these benefits come at the expense of maintaining uniformity of spot distribution inside the target volume. In this work we have developed a new optimized spot placement scheme that provides robust spot distributions inside the target. This approach achieves the boundary conformity of a concentric-contours based approach and uses a fast-iterative method to distribute the interior spots in a highly uniform fashion in an attempt to improve both the lateral dose falloff and uniformity. Furthermore, we quantified the impact of this new approach through direct comparison with grid, contour, and hybrid spot placements schemes, showing improvements for this new approach. The results were validated in homogeneous medium for two different target shapes having concave and convex geometry.

International Journal of Radiation Oncology*Biology*Physics, 2017

Purpose/Objective(s): Heterotopic ossification is a debilitating form of dystrophic calcification... more Purpose/Objective(s): Heterotopic ossification is a debilitating form of dystrophic calcification that occurs in 50-90% of patients with traumatic acetabular fractures. Radiation therapy in the peri-operative period is a proven intervention to reduce the incidence of heterotopic ossification. However, as many of the patients requiring radiation have suffered polytrauma and/or are clinically unstable, the treatment of these patients can be logistically challenging, uncomfortable for the patient and, at times, clinically unsafe. In this study, we describe the development and characterization of a clinical protocol in which the diagnostic images obtained on patients requiring radiation therapy for HO prophylaxis can be used for radiation treatment planning. This protocol allows for individualized patient treatment plans to be generated and transferred to the record and verify system prior to the patient being brought to the department for therapy. Using this method, these often times critically ill patients can be treated with improved efficiency and safety. Materials/Methods: We retrospectively identified 10 patients treated in 2015 in our department after traumatic hip fracture for heterotopic ossification prophylaxis who had undergone CT simulation for treatment planning. The diagnostic CT scans of the patients obtained by orthopedic surgery immediately post operatively to examine hardware placement were imported into the MIMvista system and corrected for orientation and then adjusted to a neutral pelvis alignment. These scans were then imported into the Pinnacle treatment planning system and plans were designed to treat the affected hip to 7.5 Gy in 1 fraction per institutional standard for HO prophylaxis. In order to determine the safety of this protocol, the treatment plans were then transferred without alteration onto the CT data set obtained at the time of CT simulation, and the dose distributions were compared. Results: There were limited differences in the dose distributions in the plans generated on the diagnostic scans and dose distributions after transfer to the CT simulation data sets. The maximum point dose was within 1% (range-1% to 1%), and the volumes receiving 7.5 Gy and 7.0 Gy were within 25% (range,-25% to 20%) and 6% (range-3% to 6%) respectively. Additionally, the treatment plans after transfer to the CT simulation data sets were each reviewed by four physicians in the department not involved in the replanning portion of the study, and 100% of the plans were felt to be appropriate for treatment. Conclusion: This study demonstrates that diagnostic imaging scans can reasonably be used to plan patients requiring radiation for heterotopic ossification prophylaxis. As a result, patients can be treated efficiently, potentially reducing the time they will spend in the department and improving patient safety.

Medical Physics, 2006

Helical tomotherapy using the Hi‐ART II is analogous to helical CTimaging where the gantry and th... more Helical tomotherapy using the Hi‐ART II is analogous to helical CTimaging where the gantry and the couch are in simultaneous motion. Hence, beam delivery is continuous over all 360 in transverse planes about the patient. Temporal beam modulation is achieved by using a binary multi‐leaf collimator. In addition to its ability to deliver IMRT, the Hi‐ART II has the ability to obtain helical megavoltage CT (MVCT) images. These MVCT images have adequate spatial and contrast resolution for image guidance, and also for identification of many soft‐tissue structures. The incorporation of daily three dimensional soft‐tissue imaging into the radiotherapy process also enables dose recalculation and periodic evaluation of the treatment delivery during a course of radiotherapy. Hence, the subsequent treatment delivery can be modified using a systematic feedback of the geometric and dosimetric information in the previous fractions. This requires many components as feedback, including CT guidance to achieve soft tissue localization, dose recalculation, dose accumulation, treatment evaluation, re‐contouring, and re‐optimization. This lecture will provide an overview of the physical characteristics of the Hi‐ART II, acceptance testing and commissioning, image quality tests, image registration, basic quality assurance, and an overview of clinical applications. Finally, system limitations and future developments will be addressed. Educational Objectives 1. Understand the basics concepts of helical tomotherapy. 2. Understand the basic QA requirements and system limitations association with helical tomotherapy. 3. Understand the workflow and issues related to clinical applications of helical tomotherapy, including acquisition, reconstruction, registration and patient alignment. 4. Understand the possibilities of daily soft‐tissue imaging for patient alignment and evaluation of treatment accuracy.

Medical Physics, 2006

Purpose: To develop a fast scan‐plan‐treat mode that can deliver breast treatments within 15 minu... more Purpose: To develop a fast scan‐plan‐treat mode that can deliver breast treatments within 15 minutes Method and Materials: With the advent of on‐line CTimaging capability, it becomes increasingly feasible to use a radiation therapy system as a single‐source device to image, plan, and deliver a patient treatment, in as little as 10–20 minutes from patient entry to exit. Such a mode can be particularly useful for cord compressions and emergency treatments. This concept is here expanded to deliver breast treatments using topotherapy, or a radiation therapytreatmentdelivered with concurrent couch motion but with a fixed gantry angle. MLC modulation may accompany this motion. The goal of this work was to explore: Whether auto‐contouring could be used to define breast and sensitive structures. Whether this process could be completed in 10‐20 minutes. The adequacy of the plans given the time constraints on both optimization and deliveryResults: It was determined that auto‐contouring could successfully contour the ipsilateral breast, the contralateral breast, each lung, and the trachea in less than 1 minute. Planning could be completed in less than 5 minutes through use of an optimization template, along with less than 5 minutes for imaging, and less than 5 minutes for delivery of 2 topographic angles. The plan optimized in this manner treated the target breast with a homogeneity of +/− 5%, and sensitive structure sparing equivalent to a conventional breast plan. Subsequent fractions can be currently created with this tool, or treated with alternate off‐line optimizations. Conclusion: The scan‐plan‐treat paradigm can be combined with a topotherapy‐style delivery to enable breast treatments in less than 20 minutes from the time a patient first enters the clinic. This work was supported by TomoTherapy Inc.

Medical Physics, 2006

ABSTRACT

Medical Physics, 2010

Optical guidance (OG) such as optical distance indicator (ODI) in‐room laser alignment and live‐v... more Optical guidance (OG) such as optical distance indicator (ODI) in‐room laser alignment and live‐video camera monitoring has been routinely used in conventional radiotherapy for patient setup and monitoring. Now emerging OG using optical tracking and topologic imaging (stereovision) techniques can provide remote operators with real‐time measurements of patient body (or support apparatus) position shape and movement. The temporal and spatial OG will be an essential component in any advanced image‐guidedradiotherapy(IGRT) when patient or organ motion are considered during the dose delivery. In assisting users to become familiar with the new OG techniques this education session will start with an introduction on basic photogrammetry general camera calibration triangulation principle for 3D optical imagingsurface extraction and registration and what OG systems can and cannot do. Then the session will move to the clinical use of infrared patient positioning and tracking systems (IPT) with particular attention to the combined use with other imagingsystems detection and correction with six degrees of freedom for rigid body displacement and issues in attachment of the infrared reflection markers. That will lead up to actual use ISG integrated stereovision‐guided patient reposition and monitoring systems focusing on quantification of the body position and displacement prior to and during beam or arc irradiation. ISG adaptive radiotherapy of the brain H&N lung and breast cancer will be demonstrated using examples from early clinical trials. The effects of target motion and deformation skin tones and room light conditions are also discussed. Learning Objectives: 1. Understand the spatial and temporal characteristics of advanced OG 2. Understand the basic operation principle of 3D optical systems 3. Know how to check and calibrate the optical camerasystems 4. Understand why multiple infrared reflection markers have to be fastened to the patient 5. Know how to quantify and correct the displacements with six‐degrees of freedom 6. Know how to surrogate optical surfaceimages with CT/MR volumetric images 7. Know how to acquire reliable surfaceimages prior to and during X‐ray irradiation 8. Understand the limits and benefits in application of OG in clinical settings

Medical Dosimetry, 1996

It is well established that the beam fluence on the central axis for rectangular or blocked field... more It is well established that the beam fluence on the central axis for rectangular or blocked fields is not always the same as that of its collimator equivalent square field. Many centers still determine monitor unit settings using a single output factor based on the collimator equivalent square field size because they feel the small errors introduced by this approach do not justify the extra data and effort required to correctly determine the monitor unit settings. Analyzing clinical monitor unit determinations for 6 and 15 MV photon irradiation. it is shown that failure to account for these discrepancies in central axis beam fluence may introduce 2.5-3% error in clinical situations. While the error is generally small, it must be eliminated if we intend to reach the commonly stated goal of 5% overall uncertainty in dose determination.

International Journal of Radiation Oncology*Biology*Physics, 2007

International Journal of Radiation Oncology*Biology*Physics, 2005

Purpose/Objective: Multiple definitions have been proposed to define successful biochemical outco... more Purpose/Objective: Multiple definitions have been proposed to define successful biochemical outcome (bNED) following definitive irradiation for prostate cancer. When the ASTRO consensus definition (ACD) and the Houston/current PSA nadir ϩ 2 (CNϩ2) definitions have been applied to the same patients treated with external beam irradiation (EBRT), substantial variation in bNED rates has been noted. The CNϩ2 definition has been reported to offer better sensitivity and specificity with regard to ultimate clinical failure. Whether or not these definitions provide similar or conflicting results when applied to prostate brachytherapy patients is uncertain. This study compares the bNED outcome using these two different definitions for patients undergoing permanent, pre-planned, transperineal ultrasound-guided interstitial I-125 prostate brachytherapy (PB), and their relationship with clinical failure (CF). Materials/Methods: 304 consecutive PB patients implanted between 1/1/98 and 3/31/01 were retrospectively evaluated. Median PSA follow-up was 52 months (maximum 80 months; 100 patients had follow-up in excess of 5 years). Patients had either low-or intermediate-risk disease. No patient received EBRT or post-PB adjuvant androgen deprivation. The prescribed dose was 144-145 Gy (TG43). The median implant activity was 40 mCi (range 24-57); the median prostate planning ultrasound volume was 38 ml (range 16-61). Median day-30 post-PB CT dosimetry values were V-100ϭ95%, V-150ϭ61%, and D-90ϭ162 Gy; median post-PB CT prostate volume was 46 ml (range 20-90). The primary endpoint for this analysis was the bNED rate determined by the ACD and CNϩ2 definitions. CF was defined as when documented local, regional, or distant recurrence developed, or when salvage hormonal therapy was initiated for biochemical failure alone. Freedom from salvage therapy (FSRx), disease-specific survival (DSS), and overall survival (OS) were also assessed. The Kaplan-Meier method was used to calculate 5-year actuarial results. Results: The 5-year bNED rate using ACD was 95%; the corresponding rate using CNϩ2 was 94%. 4 patients developed CF and all received immediate salvage androgen deprivation (SAD): 1 for distant metastasis, 1 for regional nodal failure, 1 for simultaneous local recurrence with distant metastasis; a 4th patient received SAD for biochemical failure alone. No patient experienced isolated local recurrence. There were no prostate cancer or treatment-related deaths. The 5-year FSRx rate was 98%; the 5-year DSS rate was 100%, and the 5-year OS rate was 97%. 94 (31%) of patients experienced PSA "bounce." ACD identified 15 failures; CNϩ2 identified 10 failures. This difference is due to 5 ACD failure patients with PSA nadirs between 0.2-0.5, who have, at last follow-up, slowly rising PSA values below the CNϩ2 PSA failure threshold (most recent PSA range 0.9-1.8). 3 of these 5 have undergone repeat prostate biopsies 60ϩ months post-PB; all re-biopsies were negative, and none of the 5 has regional or distant recurrence on restaging prostascint and bone scans. For detecting CF, both definitions demonstrated equal sensitivity (1.00); however, the CNϩ2 definition demonstrated higher specificity (0.98 vs 0.96), a higher positive predictive value (0.40 vs 0.27), and a higher positive likelihood ratio (50 vs 27). Conclusions: In contrast to results reported from EBRT treated patients, the ACD and CNϩ2 definitions of biochemical failure provided near-equivalent 5-year bNED rates for patients treated with PB. However, CNϩ2 more accurately identified PB patients who experienced CF and required salvage treatment.

… in Medicine and …, 2008